On Tue, Mar 03, 2020 at 04:53:19PM +0100, Joerg Roedel wrote: > On Tue, Mar 03, 2020 at 09:00:05AM -0500, Michael S. Tsirkin wrote: > > Not necessarily. E.g. some power systems have neither. > > There are also systems looking to bypass ACPI e.g. for boot speed. > > If there is no firmware layer between the hardware and the OS the > necessary information the OS needs to run on the hardware is probably > hard-coded into the kernel? No. It's coded into the hardware. Which might even be practical for bare-metal (e.g. on-board flash), but is very practical when the device is part of a hypervisor. > In that case the same can be done with > virtio-iommu tolopology. > > > That sentence doesn't really answer the question, does it? > > To be more elaborate, putting this information into config space is a > layering violation. Hardware is never completly self-descriptive This "hardware" is actually part of hypervisor so there's no reason it can't be completely self-descriptive. It's specified by the same entity as the "firmware". > and > that is why there is the firmware which provides the information about > the hardware to the OS in a generic way. > > > Frankly with platform specific interfaces like ACPI, virtio-iommu is > > much less compelling. Describing topology as part of the device in a > > way that is first, portable, and second, is a good fit for hypervisors, > > is to me one of the main reasons virtio-iommu makes sense at all. > > Virtio-IOMMU makes sense in the first place because it is much faster > than emulating one of the hardware IOMMUs. I don't see why it would be much faster. The interface isn't that different from command queues of VTD. > And an ACPI table is also > portable to all ACPI platforms, same with device-tree. > > Regards, > > Joerg Making ACPI meet the goals of embedded projects such as kata containers would be a gigantic task with huge stability implications. By comparison this 400-line parser is well contained and does the job. I didn't yet see compelling reasons not to merge this, but I'll be interested to see some more specific concerns. -- MST
